Nickel microparticle is used in such applications as an electrically conductive material and a catalyst; and it is the material drawing a keen attention in recent years. Metal microparticle such as nickel microparticle is different in its required characteristics depending on the filed in which it is used; and thus, it is considered to be necessary to control the shape of the particle in addition to control of particle diameter and crystallite diameter thereof. For example, in the electrically conductive microparticle used for electrical connection of a circuit substrate etc., in order to increase the contacting sites in the matrix as well as to enhance the electric conductivity performance, particles having projections on surface thereof are considered to be necessary. In other examples, in the case that the particle is used as a catalyst, if the particle has a larger specific surface area with the same particle diameter, better characteristics thereof can be obtained; and therefore, metal microparticles having a projection on the surface thereof is considered to be necessary.
Microparticle having an electrically conductive layer of nickel or a nickel alloy, the said electrically conductive layer having a projection form and being formed on surface of the substrate particle comprising resin microparticles, such as those described in Patent Document 1 and Patent Document 2, has been disclosed. However, in this example, fine nickel microparticles or agglomerates thereof are merely attached on the particle surface in a way of a dot-like or a string-like form. If this microparticle is laminated with the same material or composed of a different material, there are problems of delamination and of characteristic change because physical properties such as thermal expansion are different therebetween. The nickel microparticle such as the one described in Patent Document 3, which has particle diameter of 0.1 to 10 μm and on outer surface thereof a number of projections whose heights are less than ¼ relative to the particle diameter, has been disclosed; however, in this microparticle, it is difficult to keep sufficient contact because of the small projections; and therefore, it has been difficult to realize to prevent the poor conductivity, to lower the resistance value, etc.
Moreover, in any of these Documents, the study on the ratio (d/D) of a crystallite diameter (d) to a particle diameter (D) has not been carried out extensively.
Besides, in order to increase the utility as an electrically conductive slurry, it is considered to be beneficial if fusion of the particles among themselves takes place in a relatively low temperature region with the value thereof being ⅕ or less relative to the own melting point of the metal. However, actually, the investigation with regard to this point has not been carried out extensively.
In manufacturing of microparticles such as metal microparticles, it is often necessary to prevent agglomeration of the obtained microparticles among themselves; however, in the existing technologies, the agglomeration is generally prevented by use of a dispersant etc., and therefore, the status quo thereof is that this prevention of agglomeration does not come from the idea by the shape of microparticles.